Incidental Malignant Colonic Polyp Detected in a Resected Ischaemic Large Bowel: A Case Report and Literature Review

Abstract

Most patients with bowel cancer are symptomatic at the time of the diagnosis. They may present with a change in bowel habit, bleeding per rectum, abdominal pain, anaemia, weight loss or bowel obstruction. Colonic carcinoma can also be diagnosed incidentally during screening programs. Moreover, it may be incidentally detected in CT scans being performed for other indications or encountered during surgery for other causes. Some patients with colonic bowel ischaemia have associated large bowel cancer, where the ischaemic segment is usually proximal to the tumour and not necessarily associated with bowel obstruction. We are presenting a rare case of incidental malignant colonic polyp detected in a resected ischaemic large bowel in an 88-year-old gentleman. This was a very small tumour that was not visible macroscopically or detectable by imaging. Pathological examination of non-tumour colorectal resection specimens, as in this case, should include careful macroscopic examination and sequential block selection along the length of the colon, and where there is diffuse mucosal abnormality, block selection at 100mm interval is also advised. Attention to and block selection from any suspicious-looking area is warranted in all cases of non-tumour colorectal resections if such microscopic-sized malignancies of the type seen in our patient are to be picked up.

Keywords: adenocarcinoma; colonic cancer; colorectal cancer; laparotomy; lynch syndrome; malignant colonic polyp.

Figure 1. CT abdomen axial view shows free intra-peritoneal air (yellow arrow)

Figure 2. Abdominal contrast-enhanced coronal images demonstrates circumferential thickening of the descending colon with peri colonic fat stranding (A) and evidence of a few extra luminal gas locules suggesting possible site of perforation as indicated by blue arrows (A&B). There are multiple contrast-enhancing rounded structures in the root of mesentery, they represent aortobiiliac stent within the abdominal aortic aneurysm.

Figure 3. Contrast-enhanced sagittal image demonstrates diffuse circumferential thickening of the descending and proximal sigmoid colon with associated pericolonic fat stranding, in keeping with ongoing colitis. Considering the limitation due to unprepared CT scan for bowel loops evaluation, possible small intraluminal sinister polyp or mass cannot be excluded.

Figure 4. Contrast-enhanced sagittal image with magnified view demonstrates gas locules within the bowel loop wall in keeping with pneumatosis intestinalis, which is suggestive of ischaemic bowel.

Figure 5. A: H&E x10. pT3 (poorly differentiated sheet of tumour cells infiltrating pericolic adipose tissue). B: H&E x10. Cords and sheet of moderately differentiated and poorly differentiated tumour are seen in section. C: x2. Pancytokeratin (MNF116) highlighting poorly differentiated tumour component both superficially and deeply in the fat of the colon wall (red arrows). D: x4. Pancytokeratin (MNF116) highlighting tumour cells both superficially and deeply in the fat of the colon wall.

H&E: hematoxylin and eosin

Figure 6. A: x10, CDX2 uniformly negative in the poorly differentiated tumour comonent. B: x10. The poorly differentiated tumour cells are negative with CD68 immunostaining which highlights the tumour associated macrophages, as indicated by the red arrow. C: x10. The tumour is completely negative for CK7. D: x10. CK20 Showing patchy positivity of tumour in the better differentiated superficial aspect of the tumour. E: x10. CK20 The poorly differentiated aspect of the tumour is uniformly negative. The sheets of tumour cells are mostly within the red circled area.

Figure 7. A: x10. CDX2 is uniformly positive in the superficial well/moderately differentiated aspect of the tumour. B: x10. CDX2. The poorly differentiated component of the tumour is uniformly negative, mostly within the marked area. C: x4. MLH1-negative tumour (well/moderately differentiated area of glandular elements within the red marked area). D: x4. MLH1 is also diffusely negative in the poorly differentiated component.

Figure 8. A: x4. PMS2 negative in the well/moderately differentiated component. B: x10. PMS2 also negative in the poorly differentiated component. C: x10. MSH2 positive in the well/moderately differentiated component. D: x10. MSH2 is also positive in the poorly differentiated component.

Figure 9. A: x10. MSH6 is positive in the well/moderately differentiated component. B: x10. MSH6 is also positive in the poorly differentiated component.